AB0067 MODE OF ACTION AND TARGET INVESTIGATION OF THE NEW ANTI-RHEUMATIC DRUG RABEXIMOD.
Authors: G. M. Ghirardi, A. Nerviani, L. Fossati-Jimack, E. Pontarini, P. Italiani, F. Pratesi, S. Abdelmoaty, C. Högerkorp, C. Pitzalis
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Rheumatoid arthritis (RA) is a chronic systemic inflammatory autoimmune disease which primarily affects the joints <sup>[1]</sup>. Numerous agents are currently used to modify the natural course of the disease, however, several RA patients still do not reach clinical remission<sup>[2]</sup>. A recently developed quinoxaline analogue named Rabeximod (RBM) showed clinical benefits comparable to TNF-α blockers in a mouse model of collagen antibody-induced arthritis<sup>[3]</sup>. Moreover, in a phase IIa clinical trial a significantly higher clinical efficacy of RBM + Methotrexate versus Methotrexate alone has also been confirmed. <h3>Objectives</h3> Since RBM's exact biologic target has not been entirely established yet, our objective is to investigate its mode of action at the cellular and molecular level. <h3>Methods</h3> Two <i>in vitro</i> models were developed: i) Toll-like receptor (TLR)-4 and TLR-2–stimulated peripheral blood mononuclear cells (PBMCs) cultured for 24-hours and ii) Monocytes derived-macrophages (MDMs), cultured for 96-hours in persisting inflammation conditions mimicking the different phases of ACPA-positive rheumatoid synovial inflammation: recruitment, initiation, development, and persistence of the inflammatory process. PBMCs-transcriptomic analysis was performed using a NanoString nCounter SPRING Profiler (customised panel). Cytokine production was measured by ELISA. <h3>Results</h3> RBM induced dose-dependent cell mortality. Among PBMCs, monocyte viability was preferentially affected compared to lymphocytes. RBM treatment reduced IL-6 and TNF-α production both in TLR4/TLR2-stimulated PBMCs and MDMs supernatants at 24h (PBMCs) and 10-, 24-, 48- and 72-hour time-points (MDMs). RBM-induced down-regulation of IL-6 and TNF-α in PBMCs was also obtained when PBMCs were pre-incubated for 7 hours prior to TLR activation (without additional RBM), suggesting an internalisation process. After 24h, RBM induced the downregulation of several pro-inflammatory genes in TLR-4 and-2 stimulated PBMCs, including IL-6, TNF-α, CSF1, FCN1, and SPP1. Finally, after 24 hours, MDMs treated with RBM developed an altered morphology independently of the frequency of treatment exposure and the stage of inflammation. <h3>Conclusion</h3> Overall, our data suggest that RBM acts predominantly on monocytes/macrophages and can inhibit the production of pro-inflammatory molecules playing a crucial role in RA. <h3>References</h3> [1]Scherer HU, Häupl T, Burmester GR. The etiology of rheumatoid arthritis. J Autoimmun. Published online 2020. doi:10.1016/j.jaut.2019.102400 [2]Guo Q, Wang Y, Xu D, Nossent J, Pavlos NJ, Xu J. Rheumatoid arthritis: Pathological mechanisms and modern pharmacologic therapies. Bone Res. 2018;6(1). doi:10.1038/s41413-018-0016-9 [3]Hultqvist M, Nandakumar KS, Björklund U, Holmdahl R. Rabeximod reduces arthritis severity in mice by decreasing activation of inflammatory cells. Ann. Rheum Dis. 452010;69(8):1527-1532. doi:10.1136/ard.2009.121178 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Giulia Maria Ghirardi: None declared, Alessandra Nerviani: None declared, Liliane Fossati-Jimack: None declared, Elena Pontarini: None declared, Paola Italiani: None declared, Federico Pratesi: None declared, Sally Abdelmoaty Employee of: Cyxone AB, Carl Högerkorp Employee of: Cyxone AB, Costantino Pitzalis: None declared.